(i) Field of the Invention
The present invention relates to a shutter apparatus and a diaphragm apparatus incorporated in a digital camera or else. More particularly, the present invention relates to an electromagnetic actuator used as a drive source for the shutter apparatus or the diaphragm apparatus.
(ii) Description of the Related Art
When taking a photograph of an object by using a camera, a combination of an aperture diameter of a lens and a shutter time should be optimized in accordance with exposure circumstances. For such a camera, there has been a system for separately providing a diaphragm mechanism for regulating a diameter of a lens aperture, and a shutter mechanism for opening and closing the lens aperture such that these mechanisms are individually controlled. Further, in such a diaphragm mechanism, it is general to regulate a diameter of the lens aperture in two stages.
However, each of the diaphragm mechanism and the shutter mechanism requires an electromagnetic actuator, and there is a serious restriction in the cost and the space efficiency. In addition, a system capable of setting the aperture in triple or more stages is desired in the diaphragm mechanism.
In view of the above-described problems in the prior art, it is therefore an object of the present invention is to provide a shutter apparatus which can provide both of the shutter mechanism and the diaphragm mechanism. Further, it is another object of the present invention to provide a diaphragm apparatus capable of controlling an aperture in multiple stages. It is yet another object of the present invention to provide an electromagnetic actuator suitable as a drive source for the shutter apparatus and the diaphragm apparatus.
In a first aspect of the invention, an electromagnetic actuator comprises a rotor that is comprised of a permanent magnet and that is rotatable in two directions between a first end position and a second end position via an intermediate position, a coil that is wound around the rotor and that rotates the rotor in an energizing state where an electric current is applied to the coil, and auto-retaining means for retaining the rotor at one of the intermediate position, the first end position and the second end position under a non-energizing state where the electric current is not applied to the coil, wherein the auto-retaining means comprises an elastic member that regulates the rotor at the intermediate position by a mechanical elastic force, a first magnetic member that is opposed to the permanent magnet and that retains the rotor at the first end position by a magnetic attractive force, and a second magnetic member that is opposed to the permanent magnet and that retains the rotor at the second end position by a magnetic attractive force. Preferably, the auto-retaining means is designed such that the mechanical elastic force overcomes the magnetic attractive force so as to regulate the rotor at the intermediate position when the coil is switched from the energizing state to the non-energizing state while the rotor travels toward the intermediate position, further the auto-retaining means is designed such that the magnetic attractive force overcomes the mechanical elastic force so as to retain the rotor at the first end position when the coil is switched from the energizing state to the non-energizing state while the rotor travels toward the first end position, and the auto-retaining means is designed such that the magnetic attractive force overcomes the mechanical elastic force so as to retain the rotor at the second end position when the coil is switched from the energizing state to the non-energizing state while the rotor travels toward the second end position. Preferably, the coil is provided such that an amount of the electric current required for driving the rotor from the intermediate position to either of the first end position and the second end position is greater than another amount of the electric current required for driving the rotor from either of the first end position and the second end position to the intermediate position.
Further, an inventive shutter apparatus comprises a shutter blade that is arranged on a substrate having a lens aperture and that opens and closes the lens aperture, and an electromagnetic actuator that is engaged with the shutter blade and that drives the shutter blade to open and close the lens aperture, wherein the electromagnetic actuator comprises a rotor that is composed of a permanent magnet and that is rotatable in two directions between a first end position and a second end position via an intermediate position, a coil that is wound around the rotor and that rotates the rotor in an energizing state where an electric current is applied to the coil, and auto-retaining means for retaining the rotor at one of three positions selected from the intermediate position, the first end position and the second end position under a non-energizing state where the electric current is not applied to the coil, the auto-retaining means comprising an elastic member that regulates the rotor at the intermediate position by a mechanical elastic force, a first magnetic member that is opposed to the permanent magnet and that retains the rotor at the first end position by a magnetic attractive force, and a second magnetic member that is opposed to the permanent magnet and that retains the rotor at the second end position by a magnetic attractive force, and wherein the shutter blade is driven to one of three positions selected from a full opening position for opening the lens aperture, a full closing position for closing the lens aperture, and a half opening position for partially opening the lens aperture, the three positions of the shutter blade corresponding to the three positions of the rotor. Preferably, the shutter blade is selectively driven to one of the full opening position in correspondence to the first end position of the rotor, the full closing position in correspondence to the intermediate position of the rotor, and the half opening position in correspondence to the second end position of the rotor. Preferably, the shutter blade is selectively driven to one of the full opening position in correspondence to the first end position of the rotor, the half opening position in correspondence to the intermediate position of the rotor, and the full closing position in correspondence to the second end position of the rotor.
Still further, an inventive diaphragm apparatus comprises a diaphragm blade that is arranged on a substrate having a lens aperture and that regulates a diameter of the lens aperture, and an electromagnetic actuator that is engaged with the diaphragm blade to drive the diaphragm blade, wherein the electromagnetic actuator comprises a rotor that is composed of a permanent magnet and that is rotatable in two directions between a first end position and a second end position via an intermediate position, a coil that is wound around the rotor and that rotates the rotor in an energizing state where an electric current is applied to the coil, and auto-retaining means for retaining the rotor at one of three positions selected from the intermediate position, the first end position and the second end position under a non-energizing state where the electric current is not applied to the coil, the auto-retaining means comprising an elastic member that regulates the rotor at the intermediate position by a mechanical elastic force, a first magnetic member that is opposed to the permanent magnet and that retains the rotor at the first end position by a magnetic attractive force, and a second magnetic member that is opposed to the permanent magnet and that retains the rotor at the second end position by a magnetic attractive force, and wherein the diaphragm blade is driven selectively to three positions for setting the lens aperture in a large diameter, a medium diameter and a small diameter, respectively, the three positions of the diaphragm blade corresponding to the three positions of the rotor.
In a second aspect of the invention, an electromagnetic actuator comprises a rotor that is magnetized in two poles and that is rotatable in two directions between a first end position and a second end position via an intermediate position, a yoke that has a horseshoe-like shape and that is arranged relative to the rotor such that a magnetic attractive force is created when the rotor comes to either of the first end position and the second end position, a coil that is wound around the yoke and that rotates the rotor in an energizing state where an electric current is applied to the coil, and auto-retaining means for retaining the rotor at one of the intermediate position, the first end position and the second end position under a non-energizing state where the electric current is not applied to the coil, wherein the auto-retaining means comprises an elastic member that regulates the rotor at the intermediate position by a mechanical elastic force, a first stopper member that arrests the rotor at the first end position by utilizing the magnetic attractive force created between the rotor and the yoke, and a second stopper member that arrests the rotor at the second end position by utilizing the magnetic attractive force created between the rotor and the yoke. Preferably, the auto-retaining means is designed such that the mechanical elastic force overcomes the magnetic attractive force so as to regulate the rotor at the intermediate position when the coil is switched from the energizing state to the non-energizing state while the rotor travels toward the intermediate position, further the auto-retaining means is designed such that the magnetic attractive force overcomes the mechanical elastic force so as to arrest the rotor at the first end position when the coil is switched from the energizing state to the non-energizing state while the rotor travels toward the first end position, and the auto-retaining means is designed such that the magnetic attractive force overcomes the mechanical elastic force so as to arrest the rotor at the second end position when the coil is switched from the energizing state to the non-energizing state while the rotor travels toward the second end position. Preferably, the coil is provided such that an amount of the electric current required for driving the rotor from the intermediate position to either of the first end position and the second end position is greater than another amount of the electric current required for driving the rotor from either of the first end position and the second end position to the intermediate position.
Further, an inventive shutter apparatus comprises a shutter blade that is arranged on a substrate having a lens aperture and that opens and closes the lens aperture, and an electromagnetic actuator that is engaged with the shutter blade and that drives the shutter blade to open and close the lens aperture, wherein the electromagnetic actuator comprises a rotor that is magnetized in two poles and that is rotatable in two directions between a first end position and a second end position via an intermediate position, a yoke that has a horseshoe-like shape and that is arranged relative to the rotor such that a magnetic attractive force is created when the rotor comes to either of the first end position and the second end position, a coil that is wound around the yoke and that rotates the rotor in an energizing state where an electric current is applied to the coil, and auto-retaining means for retaining the rotor at one of three positions selected from the intermediate position, the first end position and the second end position under a non-energizing state where the electric current is not applied to the coil, the auto-retaining means comprising an elastic member that regulates the rotor at the intermediate position by a mechanical elastic force, a first stopper member that arrests the rotor at the first end position by utilizing the magnetic attractive force created between the rotor and the yoke, and a second stopper member that arrests the rotor at the second end position by utilizing the magnetic attractive force created between the rotor and the yoke, and wherein the shutter blade is driven to one of three positions selected from a full opening position for opening the lens aperture, a full closing position for closing the lens aperture, and a half opening position for partially opening the lens aperture, the three positions of the shutter blade corresponding to the three positions of the rotor. Preferably, the shutter blade is selectively driven to one of the full opening position in correspondence to the first end position of the rotor, the full closing position in correspondence to the intermediate position of the rotor, and the half opening position in correspondence to the second end position of the rotor. Preferably, the shutter blade is selectively driven to one of the full opening position in correspondence to the first end position of the rotor, the half opening position in correspondence to the intermediate position of the rotor, and the full closing position in correspondence to the second end position of the rotor.
Still further, an inventive diaphragm apparatus comprises a diaphragm blade that is arranged on a substrate having a lens aperture and that regulates a diameter of the lens aperture, and an electromagnetic actuator that is engaged with the diaphragm blade to drive the diaphragm blade, wherein the electromagnetic actuator comprises a rotor that is magnetized in two poles and that is rotatable in two directions between a first end position and a second end position via an intermediate position, a yoke that has a horseshoe-like shape and that is arranged relative to the rotor such that a magnetic attractive force is created when the rotor comes to either of the first end position and the second end position, a coil that is wound around the yoke and that rotates the rotor in an energizing state where an electric current is applied to the coil, and auto-retaining means for retaining the rotor at one of three positions selected from the intermediate position, the first end position and the second end position under a non-energizing state where the electric current is not applied to the coil, the auto-retaining means comprising an elastic member that regulates the rotor at the intermediate position by a mechanical elastic force, a first stopper member that arrests the rotor at the first end position by utilizing the magnetic attractive force created between the rotor and the yoke, and a second stopper member that arrests the rotor at the second end position by utilizing the magnetic attractive force created between the rotor and the yoke, and wherein the diaphragm blade is driven selectively to three positions for setting the lens aperture in a large diameter, a medium diameter and a small diameter, respectively, the three positions of the diaphragm blade corresponding to the three positions of the rotor.
The electromagnetic actuator according to the first aspect of the present invention is a moving magnet motor constituted by a rotor composed of a permanent magnet and a coil wound around the rotor. The moving magnet motor enables the rotor to be self-regulated at three points, i.e., an intermediate position, a first end position and a second end position by a combined use of the mechanical elastic force of an elastic member and the magnetic attraction force of a magnetic member. Here, auto-retaining means retains the rotor at a predetermined position in the non-energizing state where energization to the coil is shut off. The shutter apparatus according to the present invention uses as a drive source the electromagnetic actuator capable of auto-retaining the rotor at the above-described three points. A shutter blade is coupled to the electromagnetic actuator and can be shifted to three points, i.e., a full opening position, a full closing position and a half opening position in correspondence to the three points of the auto-retaining. In particular, the half opening position is associated with a small aperture state, and the present shutter apparatus serves as both the shutter mechanism and the diaphragm mechanism. Further, the diaphragm apparatus according to the present invention uses the above-described electromagnetic actuator as a drive source. The diaphragm blade is coupled with this electromagnetic actuator and can set the aperture in the three stages, i.e., large, medium and small diameters in accordance with the three points of the rotor capable of being self-regulated.
The electromagnetic actuator according to the second aspect of the present invention is a stepping motor provided with a horseshoe-like yoke. This electromagnetic actuator includes auto-retaining means and enables the rotor to be self-regulated in the non-energizing state at any of the first end position, the second end position and the intermediate position. The first end position and the second end position are placed at both ends of an operating angle of the rotor. By incorporating such an electromagnetic actuator as a drive source for the shutter apparatus, the shutter blade can be shifted to three points, i.e., a full opening position, a full closing position and a half closing position in connection with the three points of the self-regulated rotor. Utilizing the half opening position as a small aperture state causes the present shutter apparatus to have a two-stage aperture structure of the full opening position and the half opening position. The shutter apparatus serving as both the shutter mechanism and the diaphragm mechanism can be driven by the single electromagnetic actuator. Further, when this electromagnetic actuator is incorporated in the diaphragm apparatus, the diaphragm blade can be set at three points such that the diameter of the lens aperture can be regulated to be large, medium and small in accordance with the three points of the rotor capable of being self-regulated.
As a result, the aperture setting in the three stages can be realized.